Information processing difficulties are common in patients with chronic fatigue syndrome (CFS). It has been shown that the time it takes to process a complex cognitive task, rather than error rate, may be the critical variable underlying CFS patients' cognitive complaints.

The Attention Network Task (ANT) developed by Fan and colleagues may be of clinical utility to assess cognitive function in CFS, because it allows for simultaneous assessment of mental response speed, also called information processing speed, and error rate under three conditions challenging the attention system.

Comparison of data from two groups of CFS patients (those with and without comorbid major depressive disorder; n = 19 and 22, respectively) to controls (n = 29) consistently showed that error rates did not differ among groups across conditions, but speed of information processing did. Processing time was prolonged in both CFS groups and most significantly affected in response to the most complex task conditions. For simpler tasks, processing time was only prolonged in CFS participants with depression.

The data suggest that the ANT may be a task that could be used clinically to assess information processing deficits in individuals with CFS.